Quadrupeds, which go on all-fours, have the occipital foramen and cond3 les situated farther back, in proportion as the Mce is elongated. That opening, in stead of being nearly parallel to the hori zon, forms a considerable angle with it : which, measured according to Dauben ton, is of 9J degrees in the horse. The weight of the head in these animals is not therefore sustained by the spine, but by a ligament of immense strength, which is either entirely deficient, or so weak as to have its existence disputed, in the hu man subject. This ligamentum muchx, or cervical ligament, arises from the spines of the dorsal and cervical verte brx, (which are remarkably long' for that purpose,) and is fixed to the middle and posterior part of the occipital bone. It is of great size and strength in all qua drupeds, but most particularly in the ele phant; where the vast weight of the head, so much increased by the enor mous size of the tusks, sufficiently ac counts for its increased magnitude. It is bony in the mule, probably on account of the use which the animal makes of its head, in disengaging and throwing up the earth.
Animals of the genus Simia and Lemur hold a middle rank between man, who is constantly erect, and quadrupeds, whose body is supported by four extremities. l'heir structure is by no means calculat ed, like that of man, for the constant maintenance of the erect posture ; but they can support it with greater facility, and for a longer time, than other animals. Hence, in the orang-outang, the occipital foramen is only twice as far from the jaws as from the back of the head ; so that Daubenton's angle is only of 37°. It is somewhat larger in the other species of Simix, and measure in the lemur.
The general form of the cranium is most materially influenced by the direc tion, and the various degrees of promi nence, of the facial bones, To determine this with greater preci sion, Camper instituted the facial line ; the application of which is most minutely explained in his posthumous work, the natural Differences of the Features, &c." Like Daubenton, he draws un the profile of the cranium two straight lines, which intersect each other ; but in dif ferent directions from those ofthe French anatomist. An horizontal line passes through the external auditory passage and the bottom of the cavity of the nose : this is intersected by a more perpendicu lar one, proceeding from the convexity of the forehead to the most prominent point of the upper jaw, or of the inter maxillary bone. The latter is the proper facial line ; and the angle which it forms with the horizontal line determines, ac cording to Camper, the differences of the crania of animals, as well as the national physiognomy of the various races of man kind.
The two organs which occupy most of the face are, those of smelling and tasting, (including those of mastication, &c.) In proportion as these parts are more deve loped, the size of the face, compared to that of the cranium, is augmented. On the contrary, when the brain is large, the volume of the cranium is increased in proportion to that of the face. A large cranium and small face indicate therefore a large brain, with inconsiderable organs of smelling, tasting, masticating, &c. ; while a small cranium, with a large face, shew that these proportions are revers ed.
The nature and character of each ani mal must depend considerably on the relative energy of its different functions. The brain is the common centre of the nervous system. All our perceptions are conveyed to this part, as a sensorium commune : and this is the organ by -which the mind combines and compares these perceptions, and draws inferences from them ; by which, in short, it reflects and thinks. We shall find that animals partake in a greater degree of this latter faculty, or at least approach more nearly to it, in proportion as the mass of medul lary substance, forming their brain, ex ceeds that which constitutes the rest of the nervous system ; or, in other words, in proportion as the organ of the mind exceeds those of the senses. Since then the relative proportions of the cranium and face indicate also those of the brain and the two principal external organs, we shall not be surprised to find that they point out to us, in great measure, the general character of animals, the degree of instinct and docility which they pos sess. Man combines by far the largest cranium with the smallest face ; and ani mals deviate from these relations, in pro portion as they increase in stupidity and ferocity.
One of the most simple methods (though sometimes indeed insufficient) of expressing the relative proportions of these parts, is by means of the facial line, which has been already described. This angle is most open, or approaches most nearly to a right angle, in the human sub ject ; it becomes constantly more acute, as we descend in the scale from man ; and in several birds, reptiles, and fishes, it is lost altogether, as the cranium and face are completely on a level. The idea of stupidity is associated, even by the vulgar, with the elongation of the snout ; hence the crane and snipe have become proverbial. On the contrary, when the facial line is elevated by any cause which does not increase the capacity of the cra nium, as in the elephant and owl, by the cells which separate the two tables, the animal acquires a particular air of intelli gence, and gains the credit of qualities which he does not in reality possess.