1864.] MR. W. H. FLOWER ON THE BRAIN OF THE ECHIDNA. 19 
It appears from this account, that, of the cross fissures which divide 
the four tubercles in the higher mammals, the longitudinal one is 
deficient in the Monotremes, and that the bodies are ‘‘ anterior’? and 
“« posterior ” in respect to each other. Now, as in the inferior Verte- 
brates, the two optic lobes are placed laterally, and in birds widely 
separated from each other in the middle line, a deficiency of the 
median longitudinal fissure is anything but a step to the oviparous 
type; and to apply “bigeminal” to the optic lobes of the Monotre- 
mata in the same sense in which it is applied to those of the oviparous 
Vertebrates leads to an erroneous conception of their condition. 
I have lately had an opportunity of examining the brain of an 
Echidna (E. hystrix) which died in the Gardens of the Zoological 
Society ; and on exposing the optic lobes, found that they differed 
considerably in appearance from the above-quoted description. ‘They 
form together a mass transversely oblong, being *35 inch in breadth 
and *25 inch in length, placed between the optic thalami in front 
and the superior peduncles of the cerebellum behind. The small 
pineal body lies in a hollow in the middle line in front, and on each 
side of this the groove of separation between their anterior border 
and the posterior edge of the optic thalamus is distinct enough, so 
that there is no confluence of the ‘nates’ with the optic thalamus. 
On their posterior contour there is a fairly deep notch in the middle 
line, and the longitudinal fissure is indicated by a shallow groove 
along the entire upper surface. The projecting anterior and poste- 
rior tubercles on each side are also distinct, being separated from 
each other by a curved depression. The former is round, the latter 
transversely elongated, or rather crescentic, with the concavity turned 
Fig. 1. Fig. 2. 
forwards. Viewed laterally, the posterior eminence is seen to be 
somewhat less elevated than the anterior. Compared with the size 
of the cerebral hemispheres these bodies are small, much less deve- 
