The nature of the anatomical chanee which takes place in the adult individual during the periodical renewal of the antlers, is characterised by, and contemporaneous with, the following phenomena ; — a strong determination of blood to the head takes place at the spring of the year, and the vessels surrounding the frontal apophyses enlarge. This increased vascular action re sults in the secretion of a fibro-cartilagi nous matrix, manifesting itself externally by a budding, commencing at the summit of the " core," at the spot where the horns of the previous season had separated. In the early condition the horn is soft and yielding, and it is protected only by a highly vascular periosteum and delicate integument, the cu ticular portion of the latter being represented by numerous fine hairs, closely arranged. From this circumstance the skin is here termed the " velvet." As development goes on, a progressive consolidation is effected, — the ossification proceeds from the centre to the circumference and a medullary cavity is ultimately produced. While this is taking place a corresponding change is observed at the surface. The periosteal veins acquire an enormous size and by their presence occasion the formation of grooves on the subjacent bone. At the same tiine osseous tubercles, of ivory hardness, appear at the base of the stem ; these coalesce by degrees and enclose within their folds the great superficial vas cular trunks, which are thus rendered imper vious. The supply of nutriment being cut off, the first stage of exuviation is accom plished by the consequent shrivelling up and decay of the periosteal and integumentary envelopes. The full growth of the horns is now consummated, and the animals, being aware of their strength, endeavour to com plete the desquammation by rubbing them against any hard substances which may lie in their path ; this action is technically termed " burnishing." After the rutting season the horns are shed, to be again renewed in the ensuing spring.
The disposition of the horns is invariably symmetrical in a state of health, but the antlers are sometimes disproportionate on either side and their growth incomplete from deteriorating circumstances. A remarkable sympathy exists between the generative or gans and the horns, and any imperfection in the one induces a corresponding change in the other. In consequence of this reciprocal influence, the development of the horn may be arrested and the periodical shedding pre vented by castration. An illustration of this is to be seen in the cranium of a Fallow Deer preserved in the College of Surgeons' Mu seum, London. The horns of ruminants are seldom more than two in number, but ex ceptions occur in the case of the extinct Bramatherium and gigantic Sivatherium (fig. 341.) found in the tertiary deposits of Northern India. Living instances of more than a single pair are seen in the Four-horned Goat and Many-horned Sheep ; also in the Jung liburka Antelope (A. subquadricornutus) where the anterior pair are rudimentary, and in the Chousingha (A. quadricorvis), several species of which have been described by authors (flg.342.).
The structure of the horn in Cavicornua is exceedingly simple. The frontal " apophy ses " or " cores," instead of branching, form cylindrical shafts, more or less solid, the surface being protected by the ordinary peri osteum, and by an extension of true skin, the cuticular portion of which is developed into a dense horny sheath ( fig. 333.). If a trans verse section be carried through the base of the " core," a number of cavities will be ex posed, which are continuations of the frontal sinuses. These spaces do not exist in certain
of the antelopes, as for example in the Gazelle (A. dorms) and the Sasin (A. cervicapra). The horns exhibit a great variety of curve In Camelidm the bodies of the vertebrm of the neck are much lengthened (fig. 323.), but it is in the Giraffe (fig. 315.) that we see the most remarkable conformity to the cer vical type in this respect. The spinous pro cesses of this division of the column are lessened in all mammiferous animals in pro portion to the length of the cervix, and therefore we find them in the above men tioned ruminants almost entirely effaced (ex cept in the seventh vertebrm) to admit of free 'notion backward. This action is further facilitated in the Camels and in the Giraffe by the ball and socket-like conformation of the articular ends of each vertebral body, as pointed out by Profs. De Blainville and Owen. The anterior extremity of the " cen trum " is convex (fig. 344.), and the poste ture and outline, and in those of the Cabrit or Prong-horn Antelope (A. furmier), we have an approach toward the cervme type. The prong is situated about half way up, and may be considered as analogous to the brow antler ; immediately below it the root is rough, scabrous, and nodulated, being co vered also by a hairy integument (fig. 313.).
In the Buffaloes the horns acquire a pro digious size, and the cuticular sheath forms, in some instances, a thick envelope over the entire forhead.
Vertebral column and bones of the trunk. — Considerable disparity prevails in the length of different portions of the spine, depending upon the comparative elongation of the individual bones, and not upon their nurnber. The following table, selected from Cuvier, illustrates the trifling deviations in a nume rical point of view, — the seven cervicals being added and indicated in the totals : — rior concave, but there is no intervertebral synovial apparatus as seen in reptiles. The transverse processes in the short-necked t3pical ruminants are compressed, and form double " apophyses " on either side. The anterior or inferior pair are directed forward, and the posterior or superior project laterally, their common expanded base being pierced for the passage of the vertebral artery. In the latter particular, a similar arrangement obtains in the Giraffe, but the openings are placed nearer the spinal canal, because the transverse processes are feebly developed, as in all other long-necked ruminants. The Camels and Llamas do not exhibit the per foration in question. In them, the vertebral arteries enter the posterior opening of the great neural canal, external to the dura-matral sheath, and in this position they are partly lodged in a groove at the base of the superior lamina. At the anterior part of the bone this channel becomes arched over for a short space, and converted into a distinct passage (fig. 344.). The atlas in the Camels is not thus modified. In all other ruminants, in cluding the Giraffe, an opening exists in this bone, which is placed at the fore part of the superior ring. The odontoid process of the axis or dentata is well marked and prominent in the short-necked ruminantia, but the Giraffe and Camels have it very small and incorporated with the articular end of the body ; in them, also, very slight traces or transverse " apophyses " are detectable.