20 CYCLOPIA IN THE HUMAN EMBRYO. 



Wilder pictures and describes a Cyclopean pig (Wilder's fig. 1, plate 2) in 

 which the third nerve arises as a pair in the usual way, which unites after passing 

 through the superior orbital fissure. The union is in the neighborhood of the 

 orbital muscles. He also described the orbit of the cyclopean eye in a large double- 

 headed fetus. By dissection of the head he found that the two third nerves, one 

 coming from each brain, unite with each other and form a common trunk stretched 

 transversely across the midline back of the eyeball. From this anastomosis small 

 twigs arise to supply the muscles of the eyes (Wilder's fig. 6, plate 3). In his 

 work on monsters (page 282) , Ahlf eld states that Delle Chiaie described a specimen 

 having a similar anomaly, which was published in Naples in 1840. Delle Chiaie 

 gives an excellent illustration of this specimen, with a diagrammatic section of the 

 head, showing the eye and its attachments. This picture is copied by Ahlfeld on 

 plate 46, figure 18. It is somewhat difficult to identify all the structures given, 

 but he apparently pictures the two third nerves anastomosing before they reach 

 the single eye. He also pictures a branch of the fifth nerve passing into the snout, 

 which, as in our specimen, contains a cavity. I have been able to find one more 

 specimen in the literature in which there is an anastomosis of the two third nerves 

 within the orbit in cyclopia. This is in the excellent description of Dr. Black on 

 the nervous system of a cyclopean specimen at birth. Black alludes to the third 

 nerve in a single sentence. He says (on page 204) that in the region of the central 

 tendon the third nerve divides into a number of small branches, each of which com- 

 municates with its fellow on the opposite side. I have given these references, as they 

 are the only ones which I can find in the literature, and they invariably accompany 

 the description of the orbit in cyclopia. The anatomy of cyclopia in monsters 

 is rarely given; and it may be remarked that until we have numerous good 

 descriptions (like that of Black) of the eyes, central nerves, and face in cyclopia, 

 we shall not understand fully the anatomy of this most interesting type of specimen. 



In a Janus monster (No. 1178, a and &) at birth with cyclopia on one side, 

 Dr. Theodora Finney has demonstrated a large anastomosis behind the orbital 

 branches of the third nerve before they are distributed to the eye-muscles. An 

 account of her specimen with a figure is given on page 30. 



It remains to attempt to correlate what has been said above regarding 

 cyclopia with the form of the brain and the optic vesicle in early human embryos. 

 Before undertaking this attention is called to two papers by Tandler on the form 

 of the early brain in Tarshts and in Platydactylus. Tandler's papers are especially 

 noteworthy for the reason that the topography of the forebrain has been deter- 

 mined with a greater precision than has been carried out in the human embryo, 

 except possibly in the most recent work of His. There is sufficient material at 

 hand to make similar studies upon the human brain, but until this is done I must 

 content myself with what has already been published, alluding occasionally to 

 several of the specimens in our own collection. 



A specimen 3.2 mm. long, with 13 or 14 myotomes, was described with much 

 care by His in his last publication upon the brain. He has illustrated this speci- 

 men by a sagittal median section through the body as well as by the external and 



