280 
ORIGINAL ARTICLES. 
order, it will be observed, as different as possible from one expressing 
tbeir general zoological affinities. Those marked with an asterisk 
belong to the New World gronp. *Ckrysothrix , *Hapale, *Nycti- 
pithecus , Cynocephalus , m Ateles, *Cebus, Cercopithecus , Macacus , 
Man (average), Troglodytes , Tithecus , Semnopitkecus, # Pitliecia , 
* Mycetes. The extreme amount of backward projection of the cere¬ 
brum in the Saimiri ( Chrysothrix ) was first pointed out by M. Isidore 
Gieoffroy St. Hilaire,f the opposite condition and the obliquity of the 
tentorial plane in the Howling Monkey (. Mycetes seniculus ) was 
shown from a section of a skull in the Museum of the Royal College 
of Surgeons, by Mr. Huxley in the paper referred to above. 
I have now to add another term to the series, displacing the 
American Mycetes from the pre-eminence it has enjoyed for nearly 
two years, as the least occipitally developed of monkeys, and super¬ 
seding it by one, which we should scarcely have expected to find in 
such a position, viz. the Siamang ( Hylobates syndactylus—Siamanga 
syndactyla , Gray), the most highly organised of the Gibbons, a 
group ranking after the G-orilla, Chimpanzee, and the Orang, as the 
most anthropomorphous of apes. 
Our knowledge of the cerebral anatomy of the Gibbons is chiefly 
derived from the figures of the upper and under surface of the brain 
of H. syndactylus given by Sandifort, fairly executed for the time at 
which they were done, but not sufficiently exact for the requisitions 
of the present condition of science, and the figures of the cerebrum 
of II. leuciscus, by Gfratiolet, in which the cerebellum is not repre¬ 
sented. It is due to this eminent anatomist to state that, when speak¬ 
ing of the general form of the brain, he observes that, in comparing the 
adult G-ibbon’s brain with that of the Entellus monkey, a relative 
predominance of the frontal lobe is seen in the former, and of the 
occipital lobe in the latter; and that, as we descend through the 
macaques to the lowest baboons, the last named lobe gradually 
increases in development, although we are not led to conclude, from 
his description, that there is anything very remarkable in the small¬ 
ness of the occipital lobe in the Gibbon, as compared with the other 
anthropoid apes.^ 
Among a series of casts of the interior of skulls of various Mam¬ 
mals which have been lately made in the Museum of the Royal 
College of Surgeons,§ is one of an adult or rather aged specimen of 
f Archives du Museum, 1844, and the Zoologie du Voyage de la Venus, 
j Memoire sur les Plis Cerebraux de l’Homme et des Primates. Paris, 1844. 
§ These casts are made as follows:—The skull being vertically bisected (unless 
the calvarium has been removed for the purpose of taking out the brain, when no 
other incision is necessary) the small foramina and fissures are stopped with clay, 
the two halves fastened together, and the brain cavity filled through the foramen 
magnum with a composition of glue and treacle, liquid when warm, but, when cold, 
forming a firm material taking a beautiful impression of the surface with which 
