The Thorax

The bony thorax is shorter than in the horse. The inlet is higher. The roof is short, and the floor wider and relatively longer. The transverse diameter is wider in the posterior part. The summits of the spinous processes are almost in a straight line from the second thoracic to the middle of the lumbar region.

Bones of the Skull

Bones of the Cranium

The occipital bone is situated in the lower part only of the posterior surface of the skull, and is separated from the highest part (the frontal eminence) by the parietal and interparietal bones. The supraoccipital, interparietals, and parietals fuse before birth or soon after, and the mass so formed is separated from the lateral parts of the occipital bone by a transverse suture in the skull of the calf. Above this suture is a central tuberosity, to which the ligamentum nuchæ is attached, and the surface on either side is depressed and rough for muscular attachment. Below the suture the bone is much wider than that of the horse. The foramen magnum is wide, so that the condyles are further apart except below. The paramastoid processes are short and wide and are bent inward. Two constant foramina are found in the condyloid fossa; the anterior one is the hypoglossal, the other (sometimes double) conducts a vein from the condyloid canal. The latter passes upward from a foramen on the inner side of the condyle and opens into the parieto-temporal canal. The cranial surface of the supraoccipital presents a central depression, and above this is a variable but never very pronounced eminence, which corresponds to the tentorium osseum of the horse. On either side is a groove leading to the parieto-temporal canal. The basilar process is short and wide; its cranial surface is deeply concave, and the internal spheno-occipital crest is prominent. Two large tubercles below mark the junction with the sphenoid. The foramen lacerum is short and very narrow. In the adult animal the bone is excavated to contain an air-cavity which is regarded as a part of the frontal sinus.

The sphenoid bone is short. The cranial surface of the body presents a deep sella turcica, in front of which it rises abruptly. The high anterior part bears a central ridge (Rostrum sphenoidale), which joins the crista galli of the ethmoid. Two foramina occur on either side. Of these, the large anterior one is equivalent to the foramen rotundum, lacerum orbitale, and patheticum of the horse. The posterior one is the foramen ovale, which transmits the inferior maxillary nerve. The orbital wing is thick and is overlapped by the frontal in such manner as to appear externally to divide into two branches; the anterior part joins the ethmoid close to the sphenopalatine foramen, and contains a small sinus which communicates with an ethmoidal meatus. The temporal wing is small, but forms a prominent thick pterygoid crest. The pterygoid process is wide, and the pterygoid or alar foramen is absent. The sphenoidal sinus is absent in the calf and small in the adult; it communicates by one or two small openings with an ethmoidal meatus, and so with the nasal cavity.

The ethmoid bone has an extensive perpendicular plate. The lateral mass consists of five endoturbinals and eighteen ectoturbinals (Paulli). The largest ethmoturbinal is so extensive as to be termed a third or middle turbinal bone; it projects forward between the upper and lower turbinals. The lamina papyracea appears to a small extent externally in the pterygo-palatine fossa, forming part of the upper margin of the sphenopalatine foramen.

The interparietals are primitively paired, but unite before birth. As already mentioned, fusion occurs before or shortly after birth with the parietals and supraoccipital. No distinct tentorium osseum is present.

The parietal bones do not enter into the formation of the roof of the cranium. They constitute the upper part of the posterior wall, and bend sharply forward along the lateral wall, forming part of the wall of the temporal fossa. The line of inflection is marked by the prominent parietal crest, which is continuous with the temporal crest below. The parietals are excavated to form part of the frontal sinuses in the adult animal.

The condition in the young subject is as follows: The two parietals are united with each other and also with the interparietal and supraoccipital. The resulting mass is somewhat horseshoe-shaped. Its occipital part (Planum occipitale) forms the greater part of the posterior wall of the cranium and bears about its center the tuberosity for the attachment of the ligamentum nuchæ. From either side of this a line curves outward, and divides the surface into an upper smooth area and a lower area which is rough for muscular attachment. The upper border joins the frontal bone and concurs in the formation of the frontal eminence. The temporal parts (Plana temporalia) are much smaller and are concave externally; they join the frontal above and the squamous temporal below.

The frontal bones are very extensive, forming about one-half of the entire length of the skull, and all of the roof of the cranium. The posterior borders form with the parietals a large central frontal eminence (Torus frontalis), the highest point of the skull. At the junction of the posterior and the lateral borders are the processus cornu or “horn-cores,” for the support of the horns. These processes are of elongated conical form, and vary greatly in size, length, curvature, and direction. The external surface is rough and porous, marked by numerous grooves and foramina; in the fresh state they are covered by the matrix of the horns. The base has a constriction, the neck. The interior is excavated to form a number of irregular intercommunicating spaces, divided by bony septa, and communicating with the frontal sinus. In the polled breeds these processes are absent, the skull is narrower in this region, and the frontal eminence more pronounced. The supraorbital process is situated about half-way between the anterior and posterior margins; it is short and joins the frontal process of the malar bone. The supraorbital foramen (often double) is situated about an inch inward from the root of the process; it is the external orifice of the supraorbital canal (Canalis supraorbitalis), which passes downward and forward into the orbit. The foramen is in the course of the supraorbital groove (Sulcus supraorbitalis), which marks the course of the frontal vein. The anterior ends of the naso-frontal parts form a notch which receives the nasal bones, and sutural or Wormian bones are often found at this junction (naso-frontal suture). The orbital part is extensive; it is perforated behind by the orbital opening of the supraorbital canal, and below by the ethmoidal or internal orbital foramen. It does not articulate with the palatine, from which it is separated by the orbital wing of the sphenoid. The temporal part is also more extensive than in the horse. The frontal sinus is very extensive, being continued into the parietals and occipital, and the horn processes when present.

The squamous and petrous parts of the temporal bone fuse early—in fact, union is nearly complete at birth. The squamous part is relatively small. Its external surface is divided into two parts by the prominent temporal crest, which is continuous with the parietal crest above and turns forward below, ending at a tubercle above the external auditory meatus. The part behind the crest faces backward, and is partly free, partly united with the occipital. The area in front of the crest is concave and enters into the formation of the temporal fossa; it is perforated by foramina which communicate with the parieto-temporal canal. The zygomatic process is much shorter and weaker than in the horse, and articulates with the malar only. The condyle is convex in both directions. The postglenoid process is less prominent, and behind it is the chief external opening of the parieto-temporal canal. The internal surface is almost completely overlapped by the parietal and sphenoid. The petrous part proper is small, but the tympanic part is extensive. The external auditory meatus is smaller than in the horse and is directed outward. From it a plate projects downward and helps to inclose the deep depression in which the hyoid process is placed. Behind this plate is the stylo-mastoid foramen. The muscular process is large and often bifid at its free end. The bulla ossea is large and laterally compressed. It is separated from the occipital bone by a narrow opening which is equivalent to part of the foramen lacerum basis cranii of the horse. The parieto-temporal canal is formed entirely in the temporal bone. The facial canal, on the other hand, is bounded partly by the occipital bone.

Bones of the Face

The maxilla is shorter but broader and relatively higher than in the horse. Its external surface bears instead of the facial crest a rough facial tuberosity (Tuber malare), placed above the third cheek tooth; a rough curved line often extends from it to the upper part of the malar bone. The infraorbital foramen—often double—is situated above the first cheek tooth. The tuber maxillare is small, laterally compressed, and usually bears a small pointed process (Processus pterygoideus). The zygomatic process is very small. The interalveolar border is concave, and there is no alveolus for a canine tooth. The palatine process is wider, but somewhat shorter than in the horse. It incloses a large air-space, which is continuous behind with a like cavity in the horizontal part of the palate bone, forming the palatine sinus. This communicates externally (over the infraorbital canal) with the maxillary sinus; in the macerated skull it communicates with the nasal cavity by a large oval opening, which is closed by mucous membrane in the fresh state. A median septum separates the two palatine sinuses. The alveoli for the cheek teeth increase in size from before backward. The maxillary sinus proper is small and is undivided. The maxillary foramen is a narrow fissure, deeply placed at the inner side of the lacrimal bulla. The maxilla takes no part in the formation of the palatine canal. Sutural (or Wormian) bones may be found at its junction with the lacrimal and malar bones.

The body of the premaxilla is thin and flattened, and has no alveoli, since the canine and upper incisor teeth are absent. A deep notch takes the place of the foramen incisivum. The nasal process is short, convex externally, and is not closely attached to the nasal bone; the space between the two processes is greater than in the horse. The palatine process is narrow and is grooved on its nasal surface for the septal cartilage and the vomer. The palatine cleft is very wide.

The palatine bone is very extensive. The horizontal part forms one-fourth or more of the hard palate. The anterior palatine foramen opens near the junction with the maxilla, about half an inch from the median palatine suture and crest. Accessory palatine foramina are also present. The palatine groove is usually not very distinct. The palatine canal is formed entirely in this part, and there is no articulation with the vomer. A rounded ridge occurs on the nasal side of the median suture. The interior is hollow, forming part of the palatine sinus. The perpendicular part is an extensive, quadrilateral, thin plate, which forms the posterior part of the lateral wall of the nasal cavity and in part bounds the narrow posterior nares. Its internal surface is nearly flat, and is smooth and free, except behind, where it is overlapped by the pterygoid bone. The external surface is attached to a small extent to the pterygoid process behind, and is free elsewhere. The sphenopalatine foramen is a long elliptical opening, formed by a deep notch in the upper edge of the palate bone and completed by the ethmoid and sphenoid. The edge behind this foramen articulates with the orbital wing of the sphenoid, not the frontal as in the horse.

The pterygoid bone is wider than in the horse, and forms the greater part of the lateral boundary of the posterior nares. Its outer surface is almost entirely united to the palate bone and the pterygoid process, but a small part is free in the pterygo-palatine fossa. The hamulus is distinctly hook-like, thin, and sharp.

The nasal bone is little more than half the length of that of the horse. It is straight in its length, but strongly curved from side to side. It does not fuse laterally with the adjacent bones, even in old age. The posterior extremity is pointed and fits into the notch between the frontal bones. The anterior end is broader, and is divided into two parts by a deep notch. In old animals there is a small extension of the frontal sinus into this bone.

The lacrimal bone is very large. The extensive facial part is concave in its length, and bears no lacrimal tubercle. The orbital margin is marked by several notches. The orbital part forms below the remarkable lacrimal bulla; this is a large and very thin-walled protuberance, which bulges backward into the lower part of the orbit, and contains an extension of the maxillary sinus. The lacrimal fossa is small, and is just behind the orbital margin.

The malar bone is relatively long. The facial surface is extensive; it bears a curved crest (Crista facialis) just below the orbital margin, and below this it is concave from above downward. The zygomatic process divides into two branches; of these, the frontal process turns upward and backward and joins the supraorbital process of the frontal bone; the temporal process continues backward, and is overlapped by the zygomatic process of the temporal bone, completing the zygomatic arch.

The superior turbinal bone is less cribriform and fragile than in the horse, and is thickest in its middle, small at either end. It is attached to the turbinal crest of the nasal bone, and curves downward, outward, and upward to be applied outwardly to the frontal and lacrimal bones. It thus incloses a cavity which communicates with the middle meatus nasi. (In the macerated skull it opens into the frontal sinus, but this communication is closed by mucous membrane in the fresh state.)

The inferior turbinal bone is shorter but much broader than in the horse. It is attached to the maxilla by a basal lamella about an inch (ca. 2 to 3 cm.) wide, which slopes downward and inward. At the inner edge of this it splits into two plates which are rolled in opposite directions, and inclose two separate cavities, subdivided by several septa. The upper one opens into the middle meatus, the lower one into the inferior meatus nasi.

The vomer forms a wider and deeper groove than in the horse. Its anterior end rests in a groove formed by the ends of the palatine processes of the premaxillæ. The anterior third of its thin lower edge fits into the nasal crest of the maxilla; behind this it is free and separated by a considerable interval from the nasal floor.

The two halves of the mandible do not fuse completely even in advanced age. The symphyseal surfaces are extremely rough and are marked by reciprocal projections and cavities. The body is shorter, wider, and flatter than in the horse, and has eight round and relatively shallow alveoli for the lower incisors. The interalveolar border is long, curved, thin and sharp. There are no alveoli for the canine teeth, which are absent. The anterior part of the ramus constitutes a long narrow neck. The mental foramen is further forward than in the horse, and is in the posterior end of a fossa. The rami diverge more, so that the submaxillary space is wider than in the horse. They are also more strongly curved, and the angle is more pronounced. The molar part is not so high, especially in its anterior part. Its lower border is convex in its length. Its upper border bears six alveoli for the lower cheek teeth; the first is quite small, and they increase in size from before backward. The vertical part is much smaller than in the horse and its posterior border is relatively thin below, concave and wider above. The mandibular foramen is about in the middle of its inner surface, and a groove for the lingual nerve curves downward and forward from it. The condyle projects inward further than in the horse, and is concave from side to side. The coronoid process is extensive and curves backward.

The hyoid bone has a short tuberous lingual process. The middle cornua are almost, as large as the small cornua. The great cornua are narrow, except at the ends. The upper end divides into two branches, which correspond to the two angles of that of the horse. The thyroid cornua do not fuse with the body.