| OCR Text |
Show 1874.] 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 connective 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 trabecular, their sub-auditory continuations, and the inferior and internal edges of the exoccipitals, 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 trabecular; and, external to them, by the second processes (Pa2) 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 X X X I . fig. 4), which is all that represents the palato-pterygoid process of other Amphibia. Still higher up, on the inner side, the suspensorium gives off a broad, tongue-shaped, "ascending process" (a, Plate X X X . fig. 1), which mounts beneath the "third process" of the parietal bone, and applies itself to the outer side of the trabecular cartilage. The orbito-nasal (ophthalmic) division of the trigeminal nerve (V1) 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 X X I X . fig. 1 and Plate X X X I . 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 foramen 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 X X X I . 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 attachment of the suspensorium to the skull, and m a y be named the "pedicle of the suspensorium." Finally, the external and posterior angle of the suspensorial cartilage is produced upwards and backwards, on the exterior of the auditory capsule, with which it is |
