1 84 



VERTEBRATE SKELETON 



It is stated that there are no true trabecular in mammals and that the cartilage 

 here called alisphenoid is not homologous with the alisphenoid of Sauropsida, 

 but may be the same as the basipterygoid processes of reptiles. The tirst is 

 supported by the fact that the cartilages are medial to the carotid arteries. 

 The non-homology of the alisphenoids is based on the fact that these cartilages 

 in mammals lie lateral to the fifth nerves, medial to them in other \'ertebrates. 

 Neither reason seems sufficient to establish these contentions when the variabil- 



FiG. 196. — Chondrocranium of 12 mm. Talusia g-cincla (Fawcett, '21). ao, 

 ala orbitalis; at, ala temporalis; c, carotid foramen; co, cochlear part of basal plate; e, 

 endolymph foramen; eo, exoccipital; el, ethmoturbinal; h, hypophysial canal; .7, jugular 

 foramen; m, Meckelian; n, notochord; oc, otic capsule; pc, parachordal; pp, parietal 

 plate; ps, anterior paraseptal cartilage; s, orbital-nasal septum; Ina, anterior nasal 

 tectum; II, optic foramen; XII, hypoglossal foramen. 



ity of blood vessels, and the shifts which must accompany the great increase in 

 the mammalian brain are considered. Hence the older (and more natural) 

 interpretation of parts is retained here. 



The orbitosphenoid cartilage (fig. 197), connected with the pre- 

 sphenoid region, is much larger than the ahsphenoid, even in the 

 early stages of man where the reverse holds for the adult. The base 

 of each cartilage becomes perforated for the optic nerve (originally 



