78 THE SKULL AS A WHOLE. 



is continuous above with the ethmoidal cartilage, and below with the lateral cartilage of the 

 nose : this subsequently disappears. 



The malar bone also commences to ossify about the eighth week. According to Rambaud 

 and Renault it is developed from three points which have united by the fourth month of 

 fostal life ; and to the persistent separation of one of these, the divided condition of the bone 

 referred to on p. 56 may be due. 



The inferior turbinate bone is ossified in cartilage from a single centre, which only 

 appears in the fifth month. 



The inferior maxillary bone is developed principally in the fibrous tissue investing 

 Meckel's cartilage (see development of the head in VoL I.), but to a less extent the cartilage 

 itself participates in the ossification. At birth it consists of the lateral parts united at the 

 symphysis by fibrous tissue : the osseous union takes place in the first or second year. The 

 process of ossification commences very early, being preceded only by the clavicle, and proceeds 

 rapidly : it takes place from several centres, which are united by the fourth month. The 

 largest part of each half is formed from a deposit (dentary) in the membrane on the outer 

 side of Meckel's cartilage ; and to this there is added a second smaller plate (splenial) which 

 forms the inner wall of the tooth-sockets, terminating behind in the lingula. A small part of 

 the body by the side of the symphysis results from the direct ossification of the anterior end 

 of Meckel's cartilage ; and, posteriorly, the condyle and a portion of the ramus, including the 



Fig. 81. THE INFERIOR MAXILI/A OF A CHILD AT BIRTH. 

 (R. Quain.) 



a & b indicate the two portions separate at the 

 sympbysis. 



angle, are developed from another ossification in 

 cartilage. The last, however, is not connected with 

 Meckel 1 s cartilage, which can be seen in a foetus of 

 the fifth or sixth month to be prolonged up to the 



fissure of Glaser. where it becomes continuous with the slender process of the malleus, sur- 

 rounded by fibrous tissue which eventually forms the so-called internal lateral ligament of 

 the jaw. (Callender, PhiL Trans., 1869 ; Kolliker. " Entwickelungsgeschichte " ; Toldt, 

 " Wachsthum des Uiiterkiefers," Prag, 1883 ; Sutton, Trans. Odont. Soc., 1883.) 



At birth, the body of the jaw is shallow, the basal part is but little developed, and the 

 mental foramen is nearer the lower than the upper margin ; the ramus is very short and 

 oblique, the angle which it forms with the body being about 140 ; the neck of the condyle 

 also is short and inclined backwards ; and the coronoid process projects above the condyle. 

 During the succeeding years the body becomes deeper, thicker, and longer, the ramus and the 

 neck of the condyle lengthen, and the angle at which the ramus joins the body becomes less 

 obtuse, till in the adult it is nearly a right angle. In old age, consequent upon the loss of the 

 teeth and the absorption of the alveolar margin, the body becomes shallower, the mental 

 foramen opens at the upper border of the bone, and the angle is again increased. 



The hyoid bone has five points of ossification one for the body, and one for each of its 

 great and small cornua. The ossification begins in the great cornua and body in the last 

 month of foetal life, in the small cornua in the first year after birth. The great cornua and 

 body unite in middle life, the small cornua only exceptionally in advanced age. The stylo- 

 hyoid ligaments are occasionally ossified in some part of their extent. 



GENERAL MORPHOLOGY OP THE BONES OF THE HEAD 



The circumstances which contribute most to modify the form of the human skull and the 

 condition of its component bones, as compared with that of other animals, are 1st, the 

 proportionally large size of the brain and the corresponding expansion of the cranial bones 

 which enclose it ; 2nd, the smaller development of the face as a whole, and especially of the 

 jaws, which brings the facial bones almost entirely under the fore part of the brain-case, 

 instead of in front of it, as occurs in all animals, with the partial exception of the anthropoid 

 apes ; and 3rd, the adaptation of the human skeleton to the erect posture, which, as regards 

 the head, is attended with the sudden bend of the basicranial axis at a considerable angle upon 

 the line of the erect vertebral column ; and along with this the great development of the 

 cranium in a backward direction, whereby the occipito-vertebral articulation conies to be 

 placed approximately in the centre of the antero-posterior length of the skull, so that the 

 head is nearly balanced on the upper extremity of the spine. The downward openings of the 

 nostrils, the forward aspect of the orbits and eyes, the nearly vertical forehead and more or 

 less oval-shaped face, are accompaniments of these human peculiarities in the form of the 

 head, which, together with those already mentioned, strongly contrast with the smaller 



