1216 THE FCETUS. 



Ninth Week. The corpus striatum and the pericardium are first apparent. The ovary and 

 testicle can be distinguished from each other. The genital furrow appears. The osseous 

 nuclei of the bodies and arches of the vertebrae, of the frontal, vomer, and malar bones of the 

 shafts of the metacarpal and metatarsal bones, and of the phalanges appear. The union of 

 the hard palate is completed. The gall-bladder is seen. 



Third Month. The formation of the foetal placenta advances rapidly. The projection of the 

 caudal extremity disappears. It is possible to distinguish the male and female organs from 

 each other. The cloacal aperture in divided into two parts. The cartilaginous arches on the 

 dorsal region of the spine close. The points of ossification for the occipital, sphenoid, 

 lachrymal, nasal, squamous portion of temporal and ischium appear, as well as the orbital 

 centre of the superior maxillary. The pons Varolii and fissure of Sylvius can be made out. 

 The eyelids, the hair, and the nails begin to form. The mammary gland, the epiglottis, 

 and prostate are beginning to develop. The union of the testicle with the canals of the 

 Wolffian body takes place. 



Fourth Month. The closure of the cartilaginous arches of the spine is complete. Osseous 

 points for the first sacral vertebra and os pubis appear. The ossification of the malleus and 

 incus takes place. The corpus callosum, the membrana lamina spiralis, the cartilage of 

 the Eustachian tube, and the tympanic ring are seen. Fat is first developed in the sub- 

 cutaneous cellular tissue. The tonsils are seen, and the closure of the genital furrow and 

 the formation of the scrotum and prepuce take place. 



Fifth Month. The two layers of the decidua begin to coalesce. Osseous nuclei of the axis and 

 odontoid process, of the lateral points of the first sacral vertebra, of the median points of 

 the second, and of the lateral masses of the ethmoid make their appearance. Ossification 

 of the stapes and the petrous bone and ossification of the germs ot the teeth take place. 

 The germs of the permanent teeth and the organ of Corti appear. The eruption of hair on 

 the head commences. The sudoriferous glands, Brunner's glands, the follicles of the tonsil 

 and base of the tongue, and the lymphatic glands appear at this period. The differentiation 

 between the uterus and vagina becomes apparent. 



Sixth Month. The points of ossification for the anterior root of the transverse process of the 

 seventh cervical vertebra, the lateral points of the second sacral vertebra, the median points 

 of the third, the manubrium sterni and the os calcis appear. The sacro-vertebral angle 

 forms. The cerebral hemispheres cover the cerebellum. The papillae of the skin, the 

 sebaceous glands, and Peyer's patches make their appearance. The free border of the 

 nail projects from the corium of the dermis. The walls of the uterus thicken. 

 Seventh Month. The additional points of the first sacral vertebra, the lateral points of the 

 third, the median point of the fourth, the first osseous point of the body of the sternum, 

 and the osseous point for the astragalus appear. Meckel's cartilage disappears. The 

 cerebral convolutions, the island of Reil, and the tubercula quadrigemina are apparent. The 

 pupillary membrane atrophies. The testicle passes into the vaginal process of the 

 peritoneum. 

 Eighth Month. Additional points for the second sacral vertebra, lateral points for the fourth 



and median points for the fifth sacral vertebrae, can be seen. 



Ninth Month. Additional points for the third sacral vertebra, lateral points for the fifth, 

 osseous points for the middle turbinated bone, for the body and great cornu of the hyoid, 

 for the second and third pieces of the body of the sternum, and for the lower end of the 

 femur appear. Ossification of the bony lamina spiralis and axis of the cochlea takes place. 

 The eyelids open, and the testicles are in the scrotum. 



