102 



THE SKULL AND THE BONES OF THE SKULL 



Second visceral cleft Second or hyoid viscsral arch 



Third or thyrohyoid visceral arch 



OetTical sinus 



Sinus cervicalis.. 



Upper extremity 



Kxtremitas superior 



\Rudiment of tb.a heart 



Lower extremity 

 Extremitas inferior 



Umbilical duct 



Ductus omphalo-entericus 



Auditory pit 



. First visceral cleft 



Mandibular process -\ 



i. of the first or mandibular visceral arch 

 Maxillary process / 



J . Primary optic vesicle 

 Olfactory pit 



Umbilical vesicle 



Vesicula umbilicalis 



FIG. 223. HUMAN EMBRYO, FOUR WEEKS OLD. 



The umbilical vesicle has been opened. 



Parietal bone 

 Os parietale 

 Squamous portion of the temporal bone 



Squama temporalis 



Membranous portion of the primordial cranium 



Pars membranacea cranii primordialis 



Intermembranous part of the supra-occipital 



portion of the occipital bone 1 

 Pars intermembranacea squamae occipitalis 

 S i erior semicircular canal Canalis semicircularis superior - 

 Cartilaginous portion of the primordial cranium 

 Pars cartilaginea cranii primordialis 



Intercartilaginous part of the supra-occipital 



portion of the occipital bone 1 



Pars intercartilaginea squamse occipitalis 



Primitive cartilage of the petrous portion of the 



temporal bone 



Centre of ossification for the lateral portion of the 

 occipital bone (exoccipital) 1 



Centre of ossification for the basilar portion of the : 

 occipital bone (basi-occipital) 1 



1 See note to p. 57. 



Membranous portion of the primordial cranium 

 .Pars membranacea cranii primordialis 



/Greater wing 

 / Ala magna 



Squamous portion of the frontal bone 



Squama frontalis 



Centre of ossification for the lesser wing 



Cartilaginous portion of the primordial cranium 



Pars cartilaginea cranii primordialis 



(I'lanum sphenoidale) 



Nasal bone 



Os nas;Ue 



, Septum of the nose 



Sfptum nasi 



\ 



V, 



Hard palate Palatum durum 



The vomer 



Vomer 



FIG. 224. THE LEFT HALF OF THE SKULL OF A HUMAN FCETUS AT THE END OF THE FOURTH 

 MONTH (MONTHS OF FOUR WEEKS EACH). SEEN FROM WITHIN. THE CARTILAGINOUS 

 PORTION OF THE PRIMORDIAL CRANIUM (CHONDROCRANIUM) is COLOURED BLUE. 



Body-length, 4^ inches. 



Development of the Skull. 



