62 TEE BONES. 



For the petrous portion of the temporal bone there are also two small com- 

 plementary nuclei : one for the vaginal process — the base of which is united to 

 the petrous portion, and another forming the ring of the tympanum. 



Structure. — The petrous portion is the hardest mass of bone in the skeleton, 

 and scarcely contains any spongy tissue, except at the centre of the mastoid 

 process ; in the mastoid portion it may be said not to exist. 



Differential Characters in the Temporal Bone of other Animals. 



In the other domestic animals, the petrous portion of the temporal bone becomes 

 consolidated with the squamous portion, and the summit of the zygomatic process only 

 articulates with the malar bone. 



A. Ox, Sheep, Goat.— The condyle of the zygomatic process is very wide and convex in 

 every sense. The parieto-temporal canal is very large, and entirely excavated in the temporal 

 bone; its superior or internal extremity opens above the petrous portion in an excavation which 

 represents the lateral cavity of the parietal protuberance in the Horse ; at its inferior extremity 

 it always shows several orifices. 



Tiie mastoid process is very salient, and belon<^s to the squamous portion. The mastoid 

 cre.st is confounded with the upper root of the zygomatic process ; iiiferiorly, it surpasses the 

 mastoid process, and is prolonged to the mastoid protuberance. Tlie latter is very voluminous. 



The subuliform process is larger and stronger than 

 in the Horse ; there is no mastoid fissure. 



In the Sheep and Goat, the mastoid process is 

 scarcely distinct from the crest ; and the mastoid 

 portion of the bone is only at a late period consoli- 

 dated with the petrous portion. 



B. Camel. — The squamous portion of the 

 temporal is wider than that of the Horse ; it is 

 excavated in tlie upper part of its external surface. 

 The zygomatic process has a large and thin base; 

 its articular surface is nearly level from before to 

 behind, and is concave from one side to the other ; 

 the supra-condyloid process is very developed (Fig. 

 45). The petrous portion is thin, and closely con- 

 fined between the occipital and squamous bones. 

 The mastoid crest and process are not markedly 

 developed. The hyoid prolongation is placed at the 

 bottom of a great bony sheath. 



C. Pig.— The articular surface of this bone 

 resembles that of Rodents; it is not limited pos- 

 teriorly by a subcondyloid eminence, and, in addition, 

 offers a wider transverse surface. The zygomatic 

 process articulates with the jugal bone by the wliole 

 extent of its posterior border. A crest leading from 

 the external auditory hiatus to the mastoid pro- 

 The mastoid crest is, as in the Ox, confounded with 



head of the rabbit (antero-lateral 

 face). 



1, Occipital bone ; 2, parietal ; 3, tym- 

 panic bulb ; 4, auditory canal ; 8, 8, 

 nasal bones; 9, supermaxilla; 10, pre- 

 maxilla; 11, inferior maxilla. 



tuberance replaces the mastoid process, 

 the superior root of the zygomatic process. 



D. Carnivora. — In tlie Carnivora, the articular surface of the zygomatic process merely 

 forms a glenoid cavity, into which the condyle of the msixillary bone exactly fits. Tlie 

 temporal bone in these animals is alsodistinguisliedby the width of the externul auditorv canal, 

 the absence of a liyoid prolongation, the small development of the mastoid and styloid pro- 

 cesses, the enormous volume of the mastoid protuberance, and the presence of two particnlar 

 canals which cannot be traced in the other animals. One of them— the carotid mmni-tra verses 

 the mastoid portion, and joins, superiorly, the venous canal which passes between the basilar 

 process and the temporal bone ; by its inferior extremity it joins the carotid foramen, which 

 itself pern tiates the cranium, a little beyond the venous canal just mentioned. The other 

 conduit is pierced in the petrous portion immediately above the carotid canal ; it affords a 

 passage to tlie fifth pair of cranial nerves. 



E. Rabbit. --Tlie squamous portion is circular, and has a shoit process flattened from 

 before to behind at its base, and from side to side at its extremity. The articular surface is 



