518 Proceedings of tlie Association of American Anatomists 



CONTRIBUTION TO THE MOEPHOLOGY OF THE CEREBELLUM. No. 

 IV. VARIATIONS OF THE HUMAN LINGULA. By Bert B. Shroud. 



, The commonly accepted view of the lingula cerebelli is "a group of 

 four or five transverse iaminas which lie npon the middle of the val- 

 vula (velum medullar e superius)." 



This definition is true in some cases, but not in all. 



1. There may be as many as seven transverse ridges. 



2. One of the ridges may be developed into a foliated lobule. 



3. There may be only a thin layer of ectocinerea with no ridges and 

 a foliated lobule. 



ON THE CRANIAL ANATOMY OF THE PLESIOSAUEUS. By S. W. 



WiLLISTON. 



The study of a remarkably complete skull of a plesiosaur, recently 

 discovered in Kansas, has disclosed a number of interesting new facts 

 in the cranial anatomy of this order of reptiles. The brain cavity is 

 relatively large, as are also the semicircular canals; the aiisphenoid is 

 not ossified; the paroccipital (opisthotic) is completely fused in the 

 young skull; and the supraoccipitals are parial, separated by a broad 

 vacuity, containing the foramen magnum to the parietal. The single 

 temporal arcade is composed of squamosal, prosquamosal, jugal and 

 quadratojugal, representing both arcades of other reptiles. The fron- 

 tals are separated in then- whole length by an anterior prolongation of 

 the parietals. There is no separate post-orbital, lachrymal or nasal, the 

 last evidently fused with the parietal in the adult skull. The anterior 

 or membranous portion of the articular of most reptiles exists as a 

 separate ossification, confirming Baur's homologies of the reptilian 

 mandible. There is a complete and well-developed ring of sclerotic 

 ■ plates in the orbits. 



The epipterygoid joins both parietal and frontal above, in all proba- 

 bility. In three genera of plesiosaurs studied by the author, a dis- 

 tinct oval foramen was found back of the interclavicle and between the 

 clavicles, which may be called the interclavicular vacuity. He believes 

 that the interclavicle is of membranous origin and hence cannot be the 

 epi- or omosternum. 



HISTOGENESIS OF THE SENSORY NERVES OF AMPHIBIA. By Ross 

 G. Harrison. 



