THE THORAX — BONES OF THE SKULL — BONES OF THE CRANIUM 115 



cartilages. The first costal cartilages are very short; they articulate by their 

 internal surfaces with the sternum, but not with each other. 



The presence of a fourteenth rib is not very rare. It is usually floating antl may correspond 

 to an additional thoracic vertebra or to the first lumbar. Reduction of the thirteenth is more 

 common. The eighth cartilage often does not reach the sternum, but articulates with the seventh. 



The sternum consists of seven sternebrae, most of which are developed from 

 two lateral centers. It is wider, flatter, and relatively longer than in the horse, 

 and the ventral crest or "keel" is absent. The manubrium is somewhat wedge- 

 shaped and laterally compressed. Its base forms a diarthrodial joint with the 

 body of the bone, and laterally it bears extensive facets for articulation with the 

 first pair of costal cartilages. The body widens from before backward, liut behind 

 the last pair of costal facets it becomes much narrower. The ventral surface is 

 prominent on the second and third segments, concave further back. The lateral 

 borders are notched for the passage of vessels. The cariniform cartilage is absent. 

 The xiphoid cartilage is like that of the horse but is smaller. 



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 spin(nis 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 nuchse 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 (some- 

 times 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. 



