566 



ON THE THEORY OF THE VERTEBRATE SKULL 



On examining a young tadpole (fig. 9), a cartilaginous, process is seen 

 to arise from the walls of the cranium, opposite the anterior part of 

 the auditory capsule, and, passing obliquely downwards and forwards, 

 to end in a rounded condyloid head, which articulates with the repre- 

 sentative of Meckel's cartilage. At the anterior boundary of the 

 orbit the process gives off a broad, nearly vertical apophysis (O), 

 which ends superiorly in a free, rounded, and incurved edge. The 



Ail 3 



Fig. 9. — The upper right-hand figure represents a longitudinal section of the head of a Tadpole 

 just about to be hatched. The upper left-hand figure exhibits a dissection of the head 

 of a tadpole with external gills. The two lower figures represent dissections of the 

 crania of tadpoles with well-developed hinder limbs. In the one, the integuments, 

 organs of sense, &c. of the right side are taken away so as to lay bare the facial cartilages 

 and the brain. In the other the cranium is opened from above, and the brain and 

 myelon are extracted. 



The letters have the same signification as before, except My. Myelon. M. Mouth. 0//. 

 Olfactory sac. oJ>. Eye. i. Anterior cerebral vesicle. 2. Middle cerebral vesicle. 

 3. Posterior cerebral vesicle. la. Rhinencephalon. i^. Prosencephalon, ic. Deuten- 

 cephalon, or vesicle of the third ventricle. I. II. III. IV. V. Branchial arches, x. 

 Organs of adhesion. 1. Lips. 5. Trigeminal ganglion. 7. Ganglion of the portio dura. 

 8. Aperture for the exit of the pneumogastric. 



crotaphite muscle passes to its insertion on the inner side of this, the 

 so-called " orbitar process." From the condyle the cartilaginous 

 process sweeps upwards and inwards, and ends by passing into the 

 ethmo-presphenoidal cartilage. It consequently forms an inverted 

 arch, whose keystone is the condyle for Meckel's cartilage, and is, in 

 its connexions and form, strictly comparable with the cartilaginous 

 arch which I have described in the embryo fish. The posterior crus 



