Notes upon the Brain of the Alligator. 155 



(11.) The exit of the spinal accessory roots can be readily 

 found by means of the groove from which they spring. If our 

 observation be correct, the root fibres can be traced to a ganglion 

 of rather diffuse cells of the same type as those of the adjacent 

 hypoglossal nucleus. The fibres pass directly laterad to the root. 



(12.) The hypoglossal nucleus resembles the cell masses of the 

 central cornu of the cord. The cells are large and multipolar, and 

 occupy a variable area ventrad and laterad from the canalis cen- 

 tralis in tolerably definite ventral cornua. 



The fibres are easily traced to this nucleus, but no actual union 

 between fibres and cells was seen ; perhaps because of the obliquity 

 of the former. 



In conclusion, it may be mentioned that the apparent horao- 

 logues of the olivary bodies lies caudad from the crura of the cere- 

 bellum, and are of conical form with the longer diameter in the 

 antero-posterior axis. 



In horizontal section the body appears circular, and extends 

 from near the ventral surface to a high level. The structure is a 

 dense mass, containing many very small flask cells. From these 

 masses fibres ascend to the level of the ventricle. Ventral to 

 these bodies are small clustres of larger cells apparently connected 

 with the same tract. These latter clustres were at one time con- 

 sidered the roots of the seventh, but no genu of the tract could be 

 found by careful search. 



Beneath the cephalic extension of the eighth nucleus, a trans- 

 verse section exhibits many large multipolar cells, which are rare 

 elsewhere in the anterior part of the cerebellum. 



7. Measurements of an alligator brain. The following measure- 

 ments may serve instead of an extended discussion of the propor- 

 tions. 



From chiasm to end of olfactory lobes, 16 mm. 



From chiasm to front of hemisphere, 6.5 mm. 



From chiasm to posterior end of pituitary body, 8 mm. 



Combined width of hemispheres, 15 mm. 



From chiasm to anterior roots of nerve VI, 10 mm. 



Greatest width of medulla, 10 mm. 



From chiasm to anterior root of XII, 15 mm. 



Combined length of cerebrum and olfactory lobe, 20 mm. 



Median length of optic lobes, 5.5 mm. 



Median length of cerebellum, 6 mm. 



Width of cerebellum, 8.5 mm. 



