51i PROF. T. W. BEIDGK ON THE 



exoccipital (eo.) behind, the pterotic (pt.) above, with the supero- 

 lateral margin of the basioccipital (ho.) below, and in front with 

 1he prootic (pro.). The relatively large prootic (pro.) forms the 

 anterior portion of the periotic capsule, and articulates above 

 with, the sphenotic (sj)o.) and pterotic (pf.), below with the para- 

 sphenoid (ps.), and posteriorly and dorsally with the opisthotic 

 (op.), while the posterior portion of the bone forms a thin 

 squamous lamina which extends backwards, overlapping the 

 lateral surface of the basioccipital (ho.), and at the same time 

 closing in the anterior portion of the basioccipital groove. In 

 addition, the ventral portion of each prootic sends inwards a strong 

 horizontal process (PI. 37. fig. 5, pro.), which unites with its 

 fellow in the floor of the cranial cavity behind thejntuitary fossa. 

 The pterotic (PI. 37. fig. 4, pt.) constitutes the superior lateral 

 margin of the auditory capsule, and also contributes the usual 

 articular surface for the proximal extremity of the hyoman- 

 dibular ; anteriorly, the bone is in articular relation with the 

 upper surface of the prootic and with the sphenotic, and behind 

 overlaps the dorsal margin of the opisthotic. The sphenotic 

 (spo.) is a small nodular ossicle, wedged in between the upper 

 margin of the prootic and the overlapping anterior extremity of 

 the pterotic. 



As already indicated, the anterior terminatioa of each lateral 

 basioccipital groove is overlapped by the squamous posterior 

 extension of the prootic, and thus becomes converted into a 

 short, but relatively spaciou^^, bony cul-de-sac (c.s.), continuouis 

 behind wich the open portion of the groove, but terminating 

 blindly in front. The inner or cranial wall of the cul-de-sac is 

 coincident with a somewhat considerable fontanelle (PL 37. 

 fig. 5, a.f.), which is encircled above, below, and in front by the 

 prootic (pro.), and behind is limited by the anterior margin of 

 the opisthotic (op.) and by the antero- superior border of the 

 basioccipital (bo.), and in the dried skull places the cul-de-sac in 

 free communication with the cavity of the auditory capsule. The 

 formation of this auditory fontanelle is apparently due to the 

 widening of the normal sutures which separate the surrounding 

 periotic elements one from another and from the basioccipital. 

 An extremely thin fibrous membrane, which in texture, colour, and 

 appearance closely resembles the membrane closing the supero- 

 lateral cranial fontanelle, extends between the niargins of the 

 auditory fontanelle, and constitutes the only separation between 



