About 100 general practitioners on the research register of the Royal College of General Practitioners have agreed to take part in a larger study, which it is hoped will confirm these findings. This investigation is about to start, and documents to record data are being distributed. More participants will be welcome. May I, through these columns, ask interested general practitioners to write to me for further information.-I am, etc.,

Considerable work has been done on the general morphology and derivatives of the pharyngeal pouches in Reptilia. Since, however, such investigators as van Bemmelen ( '86), de Meuron ( '98), Bfauer ( '99), Prenant ( '04), and Saint-Remy ('04) have not agreed upon the embryonic topography of the reptilian pharynx, it has seemed justifiable to review the development of this region in reptiles.This investigation deals with various stages in the development of the pharyngeal region of the garter snake, Thamnophis radix (Baird and Girard), in which special attention has been given to the relative positions of the pharyngeal pouches and their derivatives, the thyroid, and the respiratory anlage.The material used was collected by Theodore Byerly and the senior author at the Fresh Water Biological Laboratory of the State University of Iowa, Lake Okoboji, 1923. Serial sections of one full-term specimen and five different embryonic stages were made. The lengths of the embryos were: 4 mm., crown-rump; 15 mm., 35 mm., 50 mm., and 80 mm. measured from crown to tip of tail.Wax models of the pharynx and its derivatives of the 4-mm.and 15-mm. embryos were constructed according to the method described by Harrison ( '24).

NINETEEN FIGURESOur knowledge of the embryological development of the horse is f a r from being complete. Few niammals have had their pharyngeal regions thoroughly investigated, and the horse has been almost completely neglected. Present-day attention on the endocrinal secretions in the human has revived a i d vitalized the interest in the pharyngeal derivatives. Since the liorse is a high-typed ungulate, with many embryological and aiiatoniical structures in cominoii with man, it is hoped that the findings of this investigation may aid in a more accurate interpretation of what is revealed in the human. The literature, even 011 the general embryological development of the horse, contains few contributions. Ewart (%) reviews this literature, mentioiling such contributors as Hausmann, Huxley, Bonnet, and Martin, whose contributions were based largely on the early embryonic membranes, with practically nothing on organologp. Ewart ('15) was able to state the accurate age of a certain horse ernbr>-o as being twenty-one days old. His drawings of appropriately selected cross-sections of this stage and the description of the structures iiivolved uridoubtedIy make a worthy contribution, but he considered the pharynx only incidentally. Robinson and Gibson ( '17) described the recoiistruction model of Ewart's twenty-one-day embryo, and this account serves as a valuable aid in interpretiiig Emart's figures. Sisson ( '21) deals adequately with the gross anatomy of the adult horse, henct: this work is accepted as a standard text in many veterinary medical schools. 233

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Serial sections of s e v~i i embryos were examined, i n four of which the cliondrocraiiia were reconstructed. l'aracliordals appcnr as independent precartilages on each side of the riotocliord i n the otie rrgiou. Later chondritieatiou occur^, nnd they fuse with the notochord. Orbitals and trabeculae appear as iiidepentlcut precartil⩾ later, as cartilages they fuse with the basal plate aiid with c a d i oilier, forininp; thr. cranial wall between the orbitul cavity uiid brain. S n alilr it shifting poster!orly of the bases of the fifth, seventh and eighth cranial nerves, in ect to the nntrrior end of the notochord a n d to t h i otic rraiclrs, occurs between the 10-inin. and the tiO-mni. xtnges. The otic vesicles, proportionately sinull i n tlie 10-nim. stage, reach their relatively largest &e in the 19-mm. embryo. The fio(irs of the otie capsules begin us lateral extensions of tlie basal plate a t the 25-mm. stage, and from these anlagen &~ndrifications extend, forming the anterior a n d posterior cuptilan.Most of the tcgmen cranii forms by cliondrifications t h a t approach the median plant! froin eucli side. I t is practically cwnplete i n the ti0-rnni. embryo. The cervical neural arches also contribute in forming the tegnicm cranii and the occipital region. The ventrally rrcnrved end of the notochnld nf the 10~1inii. stage persists tlirougli the 6O-mm. embryo. 565.JOURNAL OF MORPHOI.OOY AFD PHYSIOI.OGY, v m . 52, N o 2