754 EEPORT— 1887. 



Posterior Communicating Arteries — continued. 



Right greater than left 2S 



Left „ right IT) 



Both very small 7 



Normal ] :.'.5 



Arterial system completely normal in 76. The only abnormality i:i 4^' 

 diflference in size between the two posterior cerebral arteries. 



4. On Alteration of Iliac Divarication a7id other Changes of Pelci.- Forms 

 durin.g Growth. By Professor Cleland, F.B.S. 



It was pointed out that the iliac divarication diminishes from childhood to 

 early adult hfe, and after adult life is reached it tends again to increase. The 

 diminution was traced to the widening of the sacrum on each side opposite the 

 lower end of the auricular surface ; the later increase of the divarication is owing 

 to muscular action, and is greatest in heavily built elderly persons. 



The conjugate and transverse diameters of the pelvis are found by the author 

 to be about equal in young children, while afterwards the conjugate diameter grows 

 more rapidly than tlie transverse, till about twelve or thirteen years of ap:e, after 

 which the adult form is approached by the method pointed out by Dr. Matthews 

 Duncan. 



5. The Brain Mechanism of Smell. By Dr. Alex. Hill. 



6. The Nature and Development of the Carotid System. 

 By John Yule Mackay, M.D. 



The study of the comparative anatomy of the carotid arteries brings to light 

 a series of facts which suggest a theory of development difl'erent from that at 

 present accepted. In the mammalia the common carotid artery divides after 

 a longer or shorter course into an internal and external branch, the former supply- 

 ing the brain, the latter the rest of the head. The common carotid is regarded as 

 the portion of the truncus arteriosus stretching between the ventral ends of the 

 third and fourth foetal branchial arterial arches, its external brancli as the con- 

 tinuation of this towards the head, and the internal carotid as the third arch and 

 its dorsal prolongation to the head. The portion of the continuous dorsal vessel 

 between the third arch and the aorta, or fourth arch, has in t'le mammalia 

 disappeared in the course of development. The external carotid artery is thus 

 regarded as a ventral, the internal carotid as a dorsal, vessel. Notwithstanding 

 that in no other vertebrate group than mammals are the external carotid branches 

 gathered together into one stem distinct from the internal carotid artery, the same 

 scheme of development has been apphed to the explanation of the details in the 

 other classes, the artery supplying the brain being looked upon as the sole dorsal 

 trunk, and all the other arteries of the head as ventral. 



In the fish the blood-vessels which supply the head externally and internally 

 do not take their origin until the blood has'become arterialised after its passage 

 through the gills, and spring consequently from a dorsal trunk. In the amphi- 

 bian, however, two vessels pass forwards from the third arch, one upon the 

 ventral and the other upon the dorsal aspect of the alimentary canal. The 

 ventral vessel is small and extends no farther forwards than the tongue, while, on 

 the other hand, the dorsal artery is large and snpplies the whole of the head, its 

 branches in tiie frog being named, according to Kcker,' ' ascending pharyngeal,' 

 ' oplithalmic,' ' palatine,' and ' internal carotid.' This dorsal artery is in the young 

 amphibian in direct continuity with the aorta, but in the adult that portion of the 

 dorsal vessel between the third and fourth arches is often reduced to a solid cord. 



In the lacertilian the arrangement of the carotid vessels is similar to that in 

 the amphibian. The ventral vessel supplies the under surface of the neck and the 

 tongue, and one branch reaches as far outwards as the shoulder, and comes into 

 » AiMt. des FroscJies. Braunschwei°:, 1864. 



