78 



COMPARATIVE ANATOMY 



brain only extends as far forward as this septum, in the dorsal part 

 of which a narrow canal encloses the olfactory lobes or nerves. 



The further development of the wall of the orbital or orbito- 

 temporal fossa takes place either from the trabeculae or indepen- 

 dently of them, and during its growth, the cartilage extends 

 round a number of the cerebral nerves. The anterior ends of the 

 trabeculae, which are continuous with the ethmoidal region of the 



Internasal cavity 



Olfactory fenestra 



Antorbital process 



Prootic foramen 



Notochord 



- Ascending process} | 

 J-S 1 

 - Otic process J ^ 



Auditory caps. 



Tectum synoticum Occipital condyle 



FIG. 60. NEUROCRANITJM (PLATYBASIC TYPE) AND MANDIBULAR ARCH OF 

 LARVAL NEWT (Triton tceniatus), 2 CM. IN LENGTH, SEEN FROM ABOVE. 

 x 25. (From a model by E. Gaupp. ) 



skull, vary much in form in different Vertebrates according to 

 whether the skull is of the platy basic or tropibasic type. The 

 ethmoidal skeleton may be completed in various ways by the 

 cartilaginous nasal or olfactory capsules, the chondrifi cation of which 

 takes place independently in the connective tissue surrounding 

 the nasal sacs. Anteriorly, the ethmoidal region may extend 

 forwards to form a rostrum, or prenasal cartilages may be formed. 

 The olfactory and auditory capsules, especially in higher types, 

 then become more and more drawn in to the skull proper, and 

 the lateral edges of the basal plate begin to grow upwards round 

 the brain on both sides, eventually extending even to the dorsal 



