130 DR. T. S. COBBOLD ON THE CRANIAL BONES [April 8, 



in respect of the individual elements of which it is composed. Three, 

 or at most four, bones enclose the cranial cavity ; whilst four others 

 form the face, two being concerned in the formation of the jaws. 

 Besides these there are several osseous appendages, including the 

 hyoid apparatus. 



Commencing from behind forwards we find two lateral occipital 

 bones (A, fig. 1), forming the posterior part of the cranial vault. 

 From the side they exhibit a triangular outline ; but their bases con- 

 verge internally so as to form part of the floor of the cerebral cavity. 

 At the middle hue below, they unite, leaving, however, a small central 

 interspace, through which may be seen the posterior part of the 

 sphenoid bone ; on this latter the occipitals rest. Intimately con- 

 nected with the posterior border of these occipitals are two vertebral 

 laminte (B) supporting a single neural spine (C) ; and immediately 

 behind these there are two other laminae (D), surmounted by a double 

 neural spine (E, E). All these elements rest upon the posterior 

 part of the sphenoid bone, which may be looked upon as an ossified 

 prolongation of the chorda dorsalis. 



Opposite the point of union between the lateral occipitals and the 

 sphenoid we find two remarkable appendages (F, F). These rib- 

 like elements project obliquely backwards on either side, and form 

 cylindrical rods, having a tolerably uniform thickness throughout. 

 Notwithstanding the objections which may be raised, I am inclined 

 to regard these bones as cranial ribs. They are placed above and 

 behind the clavicular arch ; and, as Bischoff remarks in Lepidosiren 

 paradoxa, it is clear from their articular connexions that they cannot 

 be regarded as styloid processes. 



The sphenoid bone (G), seen from below (fig. 3), is spathulate. 

 "With the exception above mentioned, it forms the entire floor of the 

 cranial cavity. It is concave at the anterior half, both above and 

 beneath, and, consequently, also channeled out on either side. The 

 posterior narrow end is convex inferiorly, where it likewise displays 

 a T-shaped groove for the partial lodgement of the aorta. The 

 sphenoid is relatively longer, and terminates more abruptly in front, 

 than the corresponding bone in Lepidosiren paradoxa. 



The vault of the cranium is also for the most part covered in by a 

 single bone (H). This I believe to consist simply of the two con- 

 joined parietals ; but Bischoff thinks the frontals are likewise in- 

 cluded in the mass. The appearance of the bone very strongly mi- 

 litates against this latter view, inasmuch as two ossific centres are 

 clearly discernible at the anterior third on either side, and from these 

 two points the osseous spicules radiate in all directions. Descrip- 

 tively it may be regarded as consisting of three laminae united in the 

 central line, the two lower forming the cranial roof, and the upper 

 and somewhat thicker plate constituting a longitudinal vertical ridge, 

 analogous to the parieto-occipital crest in Carnivora. 



If the above view be correct, I think it will be admitted that the 

 singular pair of bones overlapping the parietals can be none other than 

 the frontals (I, I, figs. 1,2); but Bischoff conjecturally assumes 

 them to be the cheek-bones. That the malar bones should be found 



