26 



THE BRAIN OF THE TIGER SALAMANDER 



MENINGES, CHORIOID PLEXUSES, AND BLOOD VESSELS 



The meninges of Amblystoma were described in 1935. This account 

 shoukl be compared with that of Salamandra pubhshed in 1934 by 

 Francis, whose description was based on the investigation of Miss 

 Helen O'NeiU ('98), done under the direction of Wiedersheim and 

 Gaupp. In Amblystoma the meninges are intermediate between the 

 meninx primitiva of the lower fishes and those of the frog. Over the 

 spinal cord and most parts of the brain a firm and well-defined 

 pachymeninx, or dura, closely invests the underlying undifferenti- 

 ated pia-arachnoid. The meninges of the frog have been described by 

 others, and recently Palay ('44) has investigated their histological 

 structure in the toad. The most interesting feature of these am- 

 phibian membranes is their intimate relation with the enormous 

 endolymphatic organ described by Dempster ('30) and the associated 



blood vessels. 



The vascular supply of these brains is peculiar in several respects. 

 The distribution of arteries and veins has been described by Roofe 

 ('35, '38), and I have added some details from the adult ('35) and the 

 larva {'Md). The endocranial veins form a double portal system of 

 sinusoids of vast extent and unknown significance. Between the 

 cerebral hemispheres and the epithalamus the nodus vasculosus 

 (Gaupp) is permeated by a complicated rete of sinusoids, which re- 

 ceives venous blood from the entire prosencephalon— chorioid 

 plexuses, brain wall, and meninges. The efferent discharge from this 

 rete is by the two oblique sinuses, which pass backward across the 

 midbrain to enter a similar rete of wide, anastomosing smusoids 

 spread over the chorioid plexus of the fourth ventricle and the 

 lobules of the endolymphatic organs. This rete also receives the vems 

 from all posterior parts of the brain, meninges, and chorioid plexus. 

 The common discharge for all this endocranial venous blood is by a 

 large sinus, which emerges from the cranium through the jugular 

 foramen and joins the jugular vein. These membranous structures 

 are readily observable in the living animal without serious disturb- 

 ance of normal conditions, and they provide unique opportunities or 

 experimental study of some fundamental problems of vascular 



^\\' wSomted out by Craigie ('38, '38a, '39, '45) that within the 

 substance of this brain the penetrating blood vessels are arranged in 

 two ways-a capillary net of usual type and simple loops, which 



