66 



BONES OF THE HEAD. 



frontal process, the superior maxillaries from the maxillary lobes, and the lachrymals 

 probably from the lateral frontal lobes. 



Fig. 57. 



Fig. 58. 



Fig. 57. THE LOWER OR CARTILAGINOUS PART OF 

 THE CRANIUM OP A CHICK ON THE SIXTH DAY 

 (from Huxley, Elements of Compar. Anat. Fig. 

 57, F'). 



1, 1, chorda dorsalis ; 2, the shaded portion here 

 and forwards is the cartilage of the base of the skull ; 

 at 2 the occipital part ; at 3 the prolongations of 

 cartilage into the anterior part of the skull called 

 trabeculce cranii; 4, the pituitary space; 5, parts of 

 the labyrinth. 



Formation of the face. In studying the early 

 development of the bones of the face it is necessary 

 likewise to take into consideration the ossicles of 

 the ear, viz., the malleus, incus, and stapes ; for al- 

 though in the adult these ossicles are so minute, and 



Fig. 58. VIEW FROM BELOW OF THE CARTI- 

 LAGINOUS BASE OF THE CRANIUM WITH ITS 

 OSSIFIO CENTRES OF A HUMAN FOSTUS EIGHT 

 INCHES LONG (about five months, from Hux- 

 ley, as before, Fig. 59, slightly altered, the 

 bone being dotted to distinguish it from the 

 cartilage, which is shaded with lines). 

 1, the basilar part, 2, the condyloid or 

 lateral parts, and 3, 4, the tabular or superior 

 part of the occipital surrounding the foramen 

 magnum ; 5, centres of the pre-sphenoid on the 

 inside of the optic foramen ; 6, centres of the 

 post-sphenoid; 7, centres of the lesser wings 

 or orbito-sphenoid ; 8, septal cartilage of the 

 nose ; 9 & ] parts of the labyrinth . 



Vmjg so entirely contained within the cavity of the 

 tympanum that they have not been included 

 4 in the description of the skull, they are im- 

 portantly connected in their origin with a 



number of other bones. In each of the first three visceral arches a strip of firm tissue, 

 which becomes cartilaginous, appears. That of the first arch is the most perfect, and 

 is divided into three parts : the proximal part passes forwards some distance in 

 contact with the basis cranii, it becomes ossified without passing through a cartilagi- 

 nous stage, and from it are developed the palate bone and internal pterygoid plate ; 

 the middle part, which is very small, forms the body of the incus, and gives off two 

 processes, the long and short processes of that ossicle ; the remaining part, much the 

 largest of the three, is prolonged downwards to meet its fellow of the opposite side at 

 the extremity of the arch, and is named MecM's cartilage after its first describer. 

 (Meckel, " Handbuch der Mensch. Anat.") The upper extremity of Meckel's carti- 

 lage forms the malleus, the handle of which is developed as a process directed back- 

 wards. The lower portion is destined ultimately to dwindle away, but in the first 

 instance increases in size, and forms a rod. on the external surface of which the 

 lower jaw is formed. It can be detected on the internal aspect of the ramus of the 

 jaw, up to the eighth month of foetal life, but its only permanent vestige is the processus 

 gracilis of the malleus, which, when the tympanic cavity becomes closed inferiorly by 

 the growth of the tympanic plate, remains with its extremity fixed in the fissure of 

 Glaser. The proximal extremity of the cartilage of the second visceral arch forms 

 the stapes, and in succession downwards from this are found the stapedius muscle, 

 the styloid process of the temporal bone, the stylo-hyoid ligament, and the small 

 cornu of the hyoid bone. The only permanent portions of the cartilage of the third 

 visceral arch are the great cornu and the body of the hyoid bone. (Reichert " Ueber 



