DE. J. MUKIE OX THE MANATEE. 41 



removal of the brain I did not immediately make sections to look at the anterior parts, 

 reserving this for later on, and consequently had to immerse it in spirit. Afterwards, 

 however, I found that my previous drawings (l. c. pi. xxv. figs. 34, 35) were by no 

 means seriously inaccurate ; for I could distinguish a trace of posterior cornu, and 

 neither pineal gland, corpora quadrigemina, nor interior commissure could be said to 

 be small, as Garrod asserts ; indeed the commissure proportionally, and as compared 

 with that of the Porpoise, is large. The white matter of the corpus callosum might 

 not be absolutely so thick as I had represented in fig. 34 {l. c); but decidedly its length 

 from before backwards agreed, its splenial end reaching beyond the thalamus and in 

 part overlying the corpora quadrigemina. The walls of the lateral ventricles, in a sense, 

 are not absolutely thin, though the cavities are relatively capacious ; I could not satisfy 

 myself as to absence or presence of a septum lucidum. 



A further examination of the nerves convinces me I had not mistaken these in my 

 former memoir. Dr. Chapman (1. c. p. 454) says : — " If Dr. Murie has correctly de- 

 scribed the sixth, its origin, direction, and size are very peculiar. It is possible, how- 

 ever, that the sixth is absent in the Manatee, as I found no trace of it at its usual 

 origin. If such is the case, I should regard Murie's sixth nerve as the seventh, and his 

 eighth as the pars intermedia: his seventh would then be the eighth. I was unable to 

 trace out these nerves, being anxious to take out the brain as soon as possible. The 

 glossopharyngeal, pneumogastric, and spinal accessory were readily recognized. The 

 hypoglossal came ofl" internally, and above the position represented by Dr. Murie in 

 fig. 33, plate xxv." My fresh view of the base of the brain (PI. IX. fig. 3) shows the 

 cranial nerves as existing in the Westminster-Aquarium Manatee. Olfactory tracts 

 and bulbs are pronounced ; optics and third nerves fair-sized, and between, partially 

 hiding their deep origins, a nipple-shaped elevation, shown opened, representing pitui- 

 tary body and tuber cinereum, and apparently hiding the corpora albicantia. The 

 delicate filaments of fourth nerve, only observed in a fragmentary condition, are not 

 exhibited in the drawing. The enormous fifth nerve, commencement of its divisions, 

 and Casserian ganglion, besides the nerve's lesser root winding round the front border 

 are conspicuous, the root springing from the side of the pons. What can be no othei 

 than a good-sized sixth appears superficially to come from the pons Varolii; but in 

 reality its fibres can be traced towards the pyramidal body of the medulla oblongata. 

 To wherefore its considerable calibre in such a small-eyed Mammal, and as to its ter- 

 minal distribution within the orbit, which circumstances in this case prevented me 

 dissecting, I can only add that, piercing and ensheathed by the thick dura mater of the 

 cranial base, it passes through the great vacuity immediately behind the alisphenoid 

 adjoining the root of the fifth, and proceeds forward towards the orbital space, thus 

 somewhat militating against the notion of its being a division of the seventh nerve. 

 Moreover, what represents portio dura and portio mollis with the pars intermedia are 

 also present ; and although appearing as derivative from the pons immediately behind 



