UH 



THE CEREBRUM. 361 



The Tuber Cinereum, or Pons Tarini, is af portion of the un- 

 der surface of the crura cerebri, at the floor of the third ven- 

 tricle. It is continuous in front with the anterior margin of the 

 corpus callosum. In front of the infundibulum the optic ne/ves 

 unite, after having crossed obliquely the crura cerebri from 

 without inwards and forwards. In this passage, where they 

 reach the middle of the crura, and at the internal border of the 

 same, they come in contact with the tuber cinereum,from which 

 they get a few filaments; but of this, more hereafter. 



The Thalami Optici, called, by Gall, the Posterior Ganglions 

 of the brain, (Ganglia Postica,) are amongst the most conspi- 

 cuous parts of the internal structure of the cerebrum, and are 

 two in number, one for either side. They are situated on the 

 superior face of the crura cerebri, are about an inch and a half 

 long from behind forwards, and about eight or ten lines broad 

 and deep. 



The thalami are convex above and internally. At the junc- 

 tion of these two surfaces is observed a medullary lino, de- 

 scribed under the name of peduncle of the pineal gland. Their 

 posterior extremity is likewise convex, and is divided into three 

 rounded prominences; one is above the other two, and is the 

 Tuberculum Posterius Superius; the second is below and with- 

 in, (Corpus Geniculatum Internum,) and the third is below and 

 external, (Corpus Geniculatum Externum.) There is a fourth 

 tubercle (Tuberculum Anterius) which is situated on the upper 

 convex surface of the thalamus; it is produced by the fan-like 

 termination of a large medullary fasciculus which comes from 

 the eminentia mammillaris. 



The thalami are somewhat flattened on the middle of their 

 convex internal surface, and adhere there to each other by a 

 layer of cineritious substance, called Commissura Mollis. When 

 the brain is very slightly advanced in putrefaction, or has 

 been made soft by dropsy, this junction scarcely seems to exist 

 at all. 



The thalami are medullary on the surface presented to the 

 ventricles of the brain, but within they are a mixture of cineri- 

 tious with medullary matter. The fibres of the medullary are 

 very intimately blended with the crura cerebri, and radiate from 

 within towards the circumference of the brain: some of them 



VOL. II. 32 



