18/4.] PROF. T. H. HUXLEY ON MENOBRANCHUS. 191 



Posteriorly, each trabecula passes into the floor of a cartilaginous 

 mass, which is formed, above, by the auditory capsule, and, behind, 

 by the exoccipital, and which has undergone partial ossification. 

 But, in spite of careful search, I could find no cartilage either in the 

 supraoccipital, or in the basioccipital, region, but only a dense con- 

 nective tissue. In the midst of this, in the basioccipital region, the 

 conical extremity of the notochord is imbedded. 



The large oval space included between the trabeculse, their sub- 

 auditory continuations, and the inferior and internal edges of the ex- 

 occipitals, is floored by fibrous tissue, in which the parasphenoid is 

 developed, just as the roof of the skull is constituted by the fibrous 

 tissue in which the parietals and frontals are formed. The side 

 walls of the cranial cavity are constituted, behind, by the exoccipitals 

 and auditory capsules, in front of these, by the trabeculse ; and, 

 external to them, by the second processes (Pa 2 ) of the parietal bones. 



The suspensorial cartilage presents, anteriorly and below, an oval, 

 concave, articular facet for the articular end of Meckel's cartilage. 

 Just above this, on the inner side, is a small elevation (p, Plate XXXI. 

 fig. 4), which is all that represents the palato-pterygoid process of 

 other Amphibia. Still higher up, on the inner side, the suspenso- 

 rium gives off a broad, tongue-shaped, "ascending process" (a, 

 Plate XXX. fig. 1), which mounts beneath the "third process" of 

 the parietal bone, and applies itself to the outer side of the trabe- 

 cular cartilage. The orbitonasal (ophthalmic) division of the tri- 

 geminal nerve (V) passes beneath this tongue of cartilage, which 

 therefore, morphologically speaking, ascends higher than the eye, 

 inasmuch as the orbito-nasal nerve, as it passes forwards, runs above 

 the optic nerve (Plate XXIX. fig. 1 and Plate XXXI. fig. 4). 



The orbito-nasal nerve actually leaves the skull by a considerable 

 foramen, common to it and the other divisions of the fifth (V 2,3 ), 

 which lies between the trabecula internally and below, the pro-otic 

 externally and behind, and the parietal bone above. And this fora- 

 men is undivided ; but, as the ascending process of the suspensorium 

 passes between the orbito-nasal nerve on its inner and anterior side, 

 and the second and third divisions of the fifth on its outer and 

 posterior side, it looks as if the process in question divided the 

 foramen of exit of the trigeminal nerve into two parts. 



The ganglia of the trigeminal and of the seventh nerves are 

 situated, close together, above the trabecula, where it passes into the 

 floor of the auditory capsule — the Gasserian ganglion lying in front 

 of the anterior wall of the capsule, while the ganglion of the seventh, 

 which is very closely connected with the auditory nerve, is placed 

 rather on the ventral side of the anterior end of the capsule (Plate 

 XXXI. fig. 4). Immediately in front of these ganglia, the trabecula is 

 produced externally, and becomes continuous with the suspensorium 

 by the process (m), which thus affords the middle and chief attach- 

 ment of the suspensorium to the skull, and may be named the 

 "pedicle of the suspensorium." Finally, the external and posterior 

 angle of the suspensorial cartilage is produced upwards and back- 

 wards, on the exterior of the auditory capsule, with which it is 



