102 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxvi. 



The optic foramina (Plate 1, fig. 1, 2; Plate 2, fig. 1, 2) have been 

 correctly identified by Hatcher. Behind each of these openings 

 is another (Plate 1, fig. 1, J; Plate 2, fig. 1, 3) which he has 

 correctly called the sphenoidal fissnre. Through it passed to the 

 orbit the third nerve and possibly the fourth. This fissure, or 

 rather foramen, lies in the boundary between the orbitosphenoid 

 and the alisphenoid bones. Indeed, in our specimen the suture 

 betAveen the two bones has remained open, so that the limits of the 

 orbitosphenoidal segment may be traced. Each optic foramen is 

 in the orbitosphenoid of its side, near its hinder edge. The bones of 

 the two sides meet above the olfactory lobes and the suture is closed, 

 but over the cerebral hemisphere there is a fontanel, which was 

 closed by either the frontals or the postfrontals. As shown by 

 Hatcher's fig. 27, «Z, the orbitosphenoids met over the olfactory lobe. 

 The cerebral hemispheres and the olfactory lobes of T. serratus rested 

 on what must be regarded as the presphenoicl bone (Plate 1, fig. 1, 

 pre; Plate 2, fig. 1, pre). This is a triangular plate which, just in 

 front of the optic foramina, descends 50 mm. below the floor of the 

 brain-case, while anteriorly its free border rises to the place of exit 

 of the olfactory nerves. Its lower hinder angle is thin, but the bone 

 thickens toward the brain. Its hinder border appears to have joined 

 the basisphenoid by a suture not closed at the death of the animal. 

 Hatcher's fig. 27 shows the presphenoid of 2\ horridus. The lower 

 line leading from al is directed to it. In our specimen of T. serratus 

 the sutures between the presphenoid and the two orbitosphenoids are 

 obliterated, as they were in T. horrklus. The upper surface of each 

 orbitosphenoid is ver}'^ rough, for sutural union probably with the 

 frontals, although Hatcher's description (p. 18) and his figs. 9, 24, 

 and 27 represent the postfrontals as pushing themselves below the 

 frontals in this region. 



Above the optic foramen, opening into the upper part of the brain- 

 case and near the hinder border of the orbitosphenoid, are two 

 smaller foramina (Plate 1. fig. 1, 4? ''•/ Plate 2, fig. 1, ^ v.), the 

 one behind the other. From each, on the outer surface of the bone, 

 a groove is directed forward for a short distance. It seems probable 

 that the hinder of these gave exit to the fourth, or trochlear, nerve. 

 The anterior must have transmitted a blood-vessel. The olfactory 

 nerves (Plate 2, fig. 1, /) left the brain-case through a single orifice; 

 at least, no bony partition [Separated them as was the case with 

 T. horridus. However, near the anterior end of the olfactory canal 

 there is seen a longitudinal ridge on the upper midline, Avhich formed 

 a partial division of the olfactory lobe. The parietal formed most 

 of that part of the roof of the brain-case which covered the optic 

 lobes. Anteriorly it joined the united orbitosphenoids (Plate 2, 

 fig 1, pa). 



