in the Bones of some Frogs and Fishes. 379 



that large open space which in other frogs represents an imper- 

 fect orbita, a smaller part — the fossa temporalis. This superior 

 portion of the petrosal has moreover posteriorly a notch between 

 its prominent posterior ridge and the thick process of the ex- 

 occipital. Immediately below is the entrance of the organ of 

 hearing. The basioccipital is remarkable from its lateral branches 

 forming a rather acute anterior angle with the longitudinal axis 

 of the bone; in Cystignathus, for instance, these bi-anches are 

 directed backwards, so as to form an obtuse anterior angle ; in 

 liana and Cultripes the angle is a right one. The lateral parts 

 of the brain-capsule are entirely ossified, and apparently formed 

 by the basioccipital. The bone itself is very narrow, and its 

 lower part a slightly rounded ridge. The parietal and frontal 

 bones are not to be distinguished from one another ; they pre- 

 sent a surface equally covered with tubercles ; by emitting on 

 each side, behind the orbit, a process to meet the bony bridge 

 from the os petrosum, they appear twice as broad as between 

 the orbits ; at the latter place they are very slightly concave, 

 and three-quarters the width of the orbit. The part situated 

 in front of the orbits, and corresponding to the ossa frontalia 

 anterior a, widens again, and emits laterally an anterior bony 

 bridge to join the maxillary and the mastoid processes : this 

 bridge, likewise present in other frogs, is here very solid, and 

 covered with a granulated dermal plate furrowed by a deep 

 groove going from the anterior and inferior angle of the orbit 

 to the nasal opening, and forming a channel for a blood-vessel 

 and a nerve in the living animal ; it is more or less visible in 

 most of the species of Chelonii*. At the lower side of the skull 

 the palatine bone corresponds to the bridge described ; it is fur- 

 nished with a sharp longitudinal ridge, slightly denticulated. 

 In front of the bridge is situated the nasal opening ; irregularly 

 quadrilateral at the outside, it appears more rounded and semi- 

 circular in the cavity of the mouth. The exterior opening is 

 narrow in comparison with other frogs, as a part of it is covered 

 by a bony plate ascending from the maxillary, and as the eth- 

 moid, the anterior part of the frontal, and the maxillary form 

 one solid bridge. The ethmoid is separated from the neighbour- 

 ing bones by still visible sutures ; it is perforated in front by 

 two very distinct openings (for the n. olfactorius), and emits on 

 each side a process 5'" long and slightly arched, with the con- 

 vexity in front ; each process extends laterally to the posterior 

 end of the suture, which is formed by the maxillary and inter- 

 maxillary bones. At the outside of the skull these processes 

 are hidden beneath the bony plate in the middle of the fore- 



* Cf. e. g. the skull of Macroclemmys Temminckii, jSray, Catal. Shield 

 Kept. pi. 38. f..2. .... 



