Oateohvj}/ of the Head of llattov\a. 303 



direction from outside inwards, and to its lower circumference 

 is attached the tuberculum sphenoocci[)it;ile. 



The pleuroccipital, which in yoini<^ individuals is separated 

 by a suture truiu the paroccipital, constitutes a simple bony 

 arch. Its lower end is swollen to form the pars con<lyloidca, 

 while the upper shovel-shaped end runs out into two pointed 

 processes; by means of these it is attached to the hinder 

 surface of the paroccipital and to the supraoccipital. The 

 inner margin of the arch forms the lateral boundary of the 

 occipital foramen, from whicii the parocci[)ital is entirely 

 excluded. The external margin of the arch, which is much 

 shorter than the internal one, forms the uj)per and posterior 

 limit of the foramen jugulare, and contains from above down- 

 wards the foramen nervi hypoglossi, the foramen nervi vagi, 

 and the foramen nervi glossopharyngei. The last two nerve- 

 exits are frequently united into one externally, but internally 

 they always remain separate. 



In the representation of the occipital region of a young 

 JIatteria Fritsch * has figured the pleuroccipitals alone as the 

 lateral limiting bones of the foramen occipitale, but he adds no 

 explanation as to whether in his specimen the pleuroccipitals 

 were separated from the paroccipitals, or whether he had 

 omitted the latter merely for the sake of simplifying the 

 figure. Otherwise the outlines of the pleuroccipitals as repro- 

 duced by this author are perfectly true to nature. 



The supraoccipital is an unusually broad bony arch, which 

 extends from the occipital foramen as far as the anterior end 

 of the processus anterior superior of the otosphenoid. Upon 

 the upper curved surface there arises in a sagittal directioa a 

 low crest, the crista occipitalis, which produces the immov- 

 able connexion with the parietal. Underneath the sujjra- 

 occipital constitutes a sagittal groove, which at its hinder end is 

 contracted by the inner walls of the vestibular portion and at 

 the lower margin of which in front lies the orificium externum 

 of the aqueductus vestibuli. The posterior border has a 

 semicircular excavation and forms the upper boundary of the 

 occipital foramen. The two posterior and obliquely truncated 

 angles are expanded in the shape of hollows, and constitute on 

 each side the roof of the vestibular chamber ; they unite with 

 the pleuroecipital and paroccipital. The lateral borders come 

 into contact with the otosphenoids, while the free anterior 

 margin exhibits three projections, produced by two indenta- 



Sitzgsber. k. Akad. Wiss. Wieii, Math.-naturw. Classe, Bd. cii. Abth. i., 

 1893, p. 76. 



* Dr, A. Fritsch, " Fauna der Gaskohle uni der Kalksteine der Perm- 

 lonnatioo Bohmeas," Bd. 2, Pl•aJ,^ 1889, p. 58. 



