Lect. II.] THE duckbill's SKULL. 37 



our brain and sense capsules. But in us, as soon as it 

 is formed into proper cartilage, it is a mere basin ; in 

 many types it is a box, just open above, having there 

 a small membranous " fontanelle," as this weak part 

 was called by old anatomists. 



This chondro-cranium, or cartilaginous skuU, is very 

 massive in the Duchhill, and much of the sides and roof 

 formed by this primitive cartilage ossifies, and forms 

 part of the permanent skull, inside the familiar invest- 

 ing bones — frontal, parietal, temporal, &c. 



This is in the hinder half, but the fore part, or beak, is 

 still more remarkable as to its cartilaginous foundations. 



The general form of the hind skull, or cranium proper, 

 is intermediate between that of an Amphibian and a 

 high mammal ; the paired occipital condyles, or convex 

 cartilaginous tracts, for articulation with the first joint 

 of the neck, are large, vertical, and very much like those 

 of a Frog. But the nerves of the skull, and their 

 passages, are arranged as in the higher or gill-less types, 

 and the hypoglosssal or motor nerve of the tongue is a 

 cranial, and not a spinal nerve, as in the Frog. The 

 arched structures of the ventral aspect of the head — the 

 parts of the face and throat — are of great interest. The 

 best morphologists difi'er in the interpretation of some of 

 the details ; whilst anatomists generally, those, namely, 

 who have not been trained in Embryology, contrive to 

 make the most absurd misinterpretations of these parts. 



Here, if I fail, I shall miss both the marh and the 



