520 Mr. D. M. S. Wutson on 



III. Nerve YII. issued througli the small foramen lying 



just iu advauce of the fenestra vestibuli, which 

 agrees exactly with the corresponding foramen in 

 Sphenodoti. 



IV. Part of nerve V. must have issued througli the foramen 



in advance of the pro-otic ; whether this part in- 

 cluded both the maxillary and mandibular bi^auches 

 or only the latter will never be known. 



V. Finally, the conditions in Sphenodon, and still more in 

 Chelune, show that all the other cranial nerves issued 

 in advance of the columella cranii. 



1 have already pointed out the evidence that the internal 

 carotid passed along the side of the basisphenoid covered 

 without by the posterior ramus of the pterygoid, and finally 

 entered the pituitary fossa through its widely open side. 



No structures in Sphenodon or any other reptile give us 

 any help in discovering the function of the elaborate series 

 of canals on the walls of the brain-case which have been 

 described in detail above*. They may, however, be directly 

 compared with the series of venous canals which occur well 

 developed in Marsupials and Insectivores. 



The main canal, that which runs along the junction of the 

 parietal and columella, occupies the same position as the 

 "sinus canal ^^ described by Parker in Erinaceus, which 

 also occurs in many other Insectivores, including some 

 Zulambdodonts. 



Some of the other canals and forauiiua, including the 

 post-temporal fossa, may be analogous or homologous with 

 the many venous foramina which pierce the back of the 

 zygomatic arch in Marsupials and Insectivores. 



This old and distinguished history may be held to explain 

 the very remarkable constancy of these, often very small, 

 foramina. 



Before discussing the ear it is advisable to discover the 

 position of the digastric muscle. In reptiles this muscle, 

 which is quite superficial in position, rises from the poste- 

 rior surface of the post-temporal (squamoso-parietal) arch 

 and passes downward, covering all the muscles of the neck, 

 to be inserted iuto the post-articular part of the mandible. 

 In the Cynodont mandible, as Seeley and Broom have 



* I have recently discovered somewhat similar conditions iu Belodon, 

 Erythrosuchus, and Mydriosaurus. 



