522 Mr. D. M. S. Watson on the Cynodontia. 



clearness. A vein — the vena capitis lateralis — passes forward 

 below the paroccipital process, and turns up the anterior face 

 of that bone through the incomplete pterygo-paroccipital fossa. 

 It then splits into three, one of which rises and passes back- 

 wards and outward through the post-temporal fossa. This 

 fossa is overhung by a special flange of the squamosal, in 

 order to prevent constriction of the vein by the action of the 

 great temporal muscle. 



The second vein rises up and then turns inward and forward, 

 passing along the "sinus canal" to the orbit, but receiving 

 a vein from the brain-case through a foramen lying between 

 the parietal and prootic. 



The third branch passes directly inward and forward along 

 a groove on the upper surface of that process of the prootic 

 which joins the epi pterygoid quadrate wing, and finally passes 

 into the brain-cavity through a notch on the hinder border of 

 the epipterygoid low down in the skull. It is probable, 

 although there is no definite evidence, that the vein receives 

 another passing out of the brain-cavity through the upper 

 part of the large foramen between the front of the prootic and 

 the back of the epipterygoid. 



This venous arrangement seems to occur in all Cynodonts 

 known. 



The lower jaw of Protacmon is perfectly preserved, although 

 the splenial and coronoid region is not exposed. It agrees 

 in structure with Cynognathus (Ann. & Mag. Nat. Hist. 

 ser. 8, vol. x. p. 574), but the hinder part of the jaw is still 

 further reduced and the dentary larger. 



An interesting feature is the presence on the upper surface 

 of the surangular of a depressed roughened area adapted to 

 the inner surface of the great groove in the dentary. This 

 area extends back very nearly to the articular surface, but it 

 is certain that the dentary does not in any place touch the 

 squamosal. The extraordinarily small size of the cavity of 

 the jaw between the surangular and prearticular is vividly 

 shown by the specimen where the articular ends abruptly, the 

 cavity in front of it being only 1 mm. wide and 3 high. 



I have seen no trace of the reflected lamina, which, if 

 present, must have been very small. 



The series of Cynodonts described above cover the period 

 of time extending from the upper part of the Cisticephalus- 

 zone, of extreme Upper Permian age, to the Cynognathus-zone, 

 which is earlier than Upper Trias, and shows that very con- 



